On Magnetic Rays. 307 



it will begin to diminish in accordance with the very rapid 

 decrease of the contact-difference of aluminium and copper 

 observed in ordinary cases. It is rather remarkable that, 

 if the above theory be correct, the more electropositive a 

 metal is the less the number of bound electrons in the atom, 

 the effect of ultra-violet light should be to make a metal 

 temporarily more electronegative, as one known effect is to 

 expel electrons from the surface. It would seem as if it not 

 only projected electrons out of the surface, but projected 

 them into the atoms as well. It would be interesting to 

 investigate whether, by charging the metal positively and 

 thus preventing the expulsion of electrons, the decrease in 

 contact-difference would also be prevented. 



A rather striking experiment which, no doubt, is connected 

 with the above subject is the following. If a plate of zinc 

 or aluminium, or indeed of any metal — but the effect is more 

 marked in the case of zinc and aluminium — be exposed to 

 ultra-violet light for a short time, the light passing through 

 a geometrically shaped aperture in a screen, a distinct 

 pattern will be observed on the metal of the same shape as 

 the aperture. It was observed in the case of copper, brass, 

 silver, and platinum. 



XXVI. On Magnetic Rays. By Louis T. Moke, Professor 

 of Physics, and Edwaed <t. Bieman, M.A., Hanna Fellow 



in Physics, University of Cincinnati*. 



, , 



PROFESSOR RIGHI has applied the term "magnetic 

 rays " to certain phenomena which occur when an 

 electric current in rarefied air is influenced by a strong- 

 magnetic field. It has, of course, been known for a long 

 time that a magnetic field altered the path and appearance 

 of such currents, but it was generally believed that all the 

 effects noted were due to an orbital motion given to the 

 cathode rays by the magnetic force. Professor Righi has 

 investigated the subject most elaborately and has come to 

 the conclusion that the action of the magnetic field may give 

 rise also to a new and special kind of rays. His results 

 have appeared in numerous articles \, which have lately been 

 made more accessible by being revised and collected in a 

 book. He has not only given his own results but he has also 

 prefaced them by an account of the work of his predecessors. 



* Communicated by the Authors. 



t Mem. delta M. Accad. delV 1st. Bologna, l£08andl9C9. Le Radium 

 1910. 



X2 



